Petrol Guage Sensor - Any suggestions?

[Limey]

My petrol gauge has recently stopped working. The guage on the dash works fine (tested). I thought it might be the sensor - took it out, hooked it back up to the wiring and it works - the SECOND it goes into the tank it stops working. I can put the float all the way into the tank and it works. The second the actual sender goes into the tank it stops working. What gives here?!?! Any suggestions? What might I expect to pay for a new sender? Dont forget its an old vehicle (1983).

[Family_Dog]

I assume there is no hole in the float assembly and that it is actually mechanically working. The fuel tank sender unit comprises a variable rheostat, one side of which goes to ground (negative earth, chassis) and the other side goes to the fuel gauge unit, via the Yellow/Red wire. The schematic also shows a capacitor connected to the rheostat, which is probably there to prevent erratic readings when the petrol sloshes around the fuel tank.

Check that the sender unit is not shorting to the tank (I assume there is a gasket of some sort?) and also that the capacitor has not gone short circuit - disconnect it for this exercise.

I haven't seen the actual physical layout, but it should be easy enough to work out. Please be VERY CAREFUL of causing any sparks to appear in the near vicinity, we would hate to lose you as a member.

-F_D

[Limey]

Thanks for the reply F.D. I assumed that it was meant to go to earth via the fuel tank because there was only 1 wire attached to the sender. It worked perfectly before, then suddenly stopped. The thing is - when I attach the lead to the terminal, and touch the actual sender body to the frame work of the vehicle, then it works fine. It seems to be earthing through the petrol though, if this is even possible??

[BenHur]

Try earthing the unit when installed in place by running a wire from a screw that secures the unit to a place on the chassis to make sure it is earthed properly. Your tank's existing earth may not be good anymore.

[Family_Dog]

Yep, I was wondering whether the "live" wire was shorting to earth, but it could obviously be an earthing problem as well. I assumed (Ugh!) you were earthing it against the tank after removing it for testing and when it worked.

-F_D

[BenHur]

A short (sense wire to earth) would cause a full deflection on the gauge i.e. it would give you a "full tank" reading.

If the gauge is not working it is due to a disconnection and not a short.

[Family_Dog]

Aaahhh... My gauge works just fine, so my guess work was not too good then, was it?

-F_D